Preparation

1- I have bare plasterboard. Can I apply a mix of 3:1 pva-water and plaster when tacky ?.

2- I have some plastered walls, previously painted. Do I seal them with a 1:5 pva-water mix and when dry continue as in No.1 above ?.

3-I have some bonding plaster on the wall which is totally dry. Do I seal this with PVA mix ?. BTW do you normally apply the finishing plaster to undercoat the same day whilst it is still wet ?.

4- I have some one coat plaster on one wall, again totally dry. Does the same apply as No.3 above ?.

Answer

1. The plasterboard does not need to have any PVA applied - you are fine to just apply the plaster direct. However if the plasterboard is old or you are concerned for any other reason -then applying PVA will not cause any problems.

2.Yes apply a diluted coat of PVA then when it has gone tacky apply a small amount of plaster (just a small area of a couple of inches) and leave for a few minutes. If it starts to become dry during this time then the wall is still too porous and you need to apply another coat of diluted PVA and test again. (If in doubt put another coat on otherwise you risk the wall drying to quickly before you have a chance of finishing it properly.

3. Yes same as No.2 above. Yes normally it is nice to apply the skim coat, to a backing coat the next day - however it may still need sealing with PVA or soaking down with water. Applying a small amount of plaster to test the suction is always a good idea.

4. Yes apply PVA and test suction etc.

Comments for Preparation

Hi, I am in the process of remodeling my home and now have stud plasterboard walls joining block plastered walls. The difference in the thickness is less than 5mm so I was thinking of a skim coat. I was hoping to get away with plastering up to the join. Is this possible, or is it best to skim the joining wall too? If so how is this painted wall to be treated so it accepts the plaster.

Many thanks

AnswerThe painted wall needs to have a diluted coat of PVA applied to it. If the wall you are joining up to is large then join, if small then it will be quicker to plaster both areas (in which case feather out the join first so this extra thickness has a chance to firm up before plastering as one).